Sharpening a Japanese knife

Do you need to soak the stone first?

It depends on the stone rather than being one rule for every brand. Wikipedia's overview of knife sharpening explains that Japanese water stones, natural and artificial alike, are traditionally soaked in water before use, then flushed with water occasionally during sharpening so the stone's pores do not clog. Some of what we stock still works that way: our Imanishi Dragon 800 grit stone is a soaking stone, and the Imanishi Kitayama 8000 grit finishing stone wants about 15 minutes of soaking before use. Naniwa's Chosera range, by contrast, only needs soaking if you want to, up to about 15 minutes, and Shapton's RockStar range is splash and go, wet the surface and start sharpening, no soak at all. Check the specific stone rather than assuming.

What angle do you actually sharpen at?

There is a range rather than one number, and it depends on the maker and the blade. Tojiro's own sharpening guide has you position the blade at roughly 45 degrees across the stone, then tilt the edge itself to about 15 degrees for a double bevel blade, lifting the angle slightly on the back side. Wikipedia's overview of knife sharpening puts East Asian kitchen knives generally in a 15 to 18 degree range per side, next to 20 to 22 degrees for a typical Western blade, since a shallower angle cuts finer but chips more easily under side load. A single bevel deba or yanagiba is different again: Tojiro's guide has you rest the kiriha, the beveled face itself, flat on the stone and work it back and forth, rather than tilting the spine the way you would on a double bevel knife.

How do you know when you have raised a burr?

A burr is the sign that you have actually reached the edge rather than just polishing the bevel above it. Tojiro's own guide has you check the back of the blade for a burr after working each section, then move on once you can feel one the whole way along, leaving only the last stretch near the heel a little less keen on purpose. Run a finger lightly across the edge, never along it, and you should feel a slight, even ridge rather than a smooth taper. Once a burr runs the full length, flip the knife and sharpen the back lightly, just enough to remove it, and that grit is done.

What grit do you need, and in what order?

Move from coarse to fine rather than starting on a finishing stone, and stop once the edge does what you need. Wikipedia's entry on sharpening stones sets out the traditional Japanese grading in three rough bands: ara-to, a rough stone, roughly 500 to 1000 grit on a non-Japanese numbering system; naka-to, a middle stone, roughly 3000 to 5000 grit; and shiage-to, a finishing stone, roughly 7000 to 10000 grit. What we stock maps onto that fairly closely. Naniwa's Chosera and Gouken Arata ranges cover 400 grit for establishing a new bevel or removing chips and 800 grit for routine resharpening, with 3000 and 5000 grit for refining the edge further; our Imanishi Dragon 800 grit stone sits in that same middle band. For finishing, we stock the Imanishi Kitayama and Naniwa Junpaku Snow White at 8000 grit, the Naniwa Gouken Arata at 10000 grit and Shapton's RockStar at 8000 and 16000 grit. A single stone around 800 to 3000 grit is enough to keep a knife going between full sharpens; the stones either side of that are for a chipped edge or a mirror finish, not routine touch ups. Our whetstone guide covers exactly what we have on the shelf, grit by grit.

Do you need to flatten the stone?

Yes, eventually, and Wikipedia's entry on sharpening stones explains why: a whetstone wears unevenly with use, typically hollowing out in the middle, so a knife sharpened on a dished stone develops an uneven edge as a result. A flattening stone or a diamond plate rubbed across the surface levels it back out. We stock two ways to do this: Suehiro's ceramic flattening stones in a coarse and a medium cut, a cheaper option the listing itself calls the budget choice next to a diamond plate, and Atoma's diamond flattening plates at 140 and 600 grit, built with a handled aluminium base so the plate does not stick to the stone as it flattens it.

What about stropping?

A strop is the last step after your finest stone, not a replacement for one. Wikipedia's overview of knife sharpening describes stropping as a finishing step done on a leather strap, sometimes bare and sometimes loaded with a fine abrasive compound, that removes little or no metal but straightens or very slightly reshapes the edge; a stropped blade can come back to what the same overview calls like new condition without another trip to the stones. We do not currently stock a dedicated leather strop, so the practical version is your finest waterstone: a few very light passes with almost no pressure does much the same job.

How do you look after it between sharpens?

Daily care is what keeps a knife off the stones as long as possible. Tojiro's own maintenance guide is direct: wash with a soft sponge and neutral detergent, rinse well, then dry the blade fully rather than leaving it wet, since salt or acid left on the steel and damp storage are both named as causes of rust. Never put a Japanese knife in a dishwasher; Wikipedia's overview of knife sharpening lists dishwasher heat and corrosive chemicals alongside acid from lemons or tomatoes as ways a blade gets damaged without ever touching a stone. The same overview names a second, separate cause: using the knife as a scraper or a pry bar, which loads the tip sideways and bends the edge rather than cutting cleanly through it, so lever nothing with the blade. The Sakai Takayuki care note for this santoku adds a third: no frozen food, since a hard, cold surface can chip a thin edge much the way a glass or stone cutting board can. Wikipedia's own entry on cutting boards is blunt about that board choice: a knife edge can be blunted by too abrasive a surface and chipped by one that is too hard, so a soft, non-abrasive material such as a wooden board suits a sharp edge far better than glass. Carbon blades need one more step: rinse and dry as you finish cutting, then a light coat of oil before the knife goes back in the drawer, since the exposed edge will discolour and can rust without it.

Quick answers

These are the questions people ask us most often about sharpening a Japanese knife, answered briefly.

Do I need to soak every whetstone before I use it? No. Traditional Japanese water stones and some of what we stock, like the Imanishi Dragon and Kitayama, want a soak first; Naniwa's Chosera range only needs one if you want it, and Shapton's RockStar range is splash and go with no soaking at all.

What angle should I sharpen at? Tojiro's own guide tilts a double bevel edge to about 15 degrees against the stone; Wikipedia's overview of knife sharpening puts East Asian kitchen knives generally between 15 and 18 degrees per side, shallower than 20 to 22 degrees for a Western blade. A single bevel knife is sharpened flat on its beveled face instead.

How do I know the edge is actually sharp enough? Feel for a burr, a slight, even ridge along the whole edge, rather than judging by eye. Check the back of the blade for it after each section, move on once you feel one, then flip the knife and sharpen the back lightly to remove it.

Can a Japanese knife go in the dishwasher? No. Tojiro's own maintenance guide says to hand wash and dry a knife fully rather than leave it wet, and Wikipedia's overview of knife sharpening names dishwasher heat and chemicals as one of the ways a blade gets damaged outside of cutting.

Do I need a leather strop? Not strictly. Stropping straightens and slightly polishes an edge after your finest stone, but a few very light passes on that same finishing stone does much the same job if you do not have a dedicated strop.